Hello everybody, Here is an interesting blog post from yosefk about Forth and stack machines:
http://yosefk.com/blog/my-history-with-forth-stack-machines.html It contains a lot of interesting stuff but one part in particular got my interest. He is trying to write a word to "compute the mean and the standard deviation of a vector given the sum of its elements, the sum of their squares, and the inverse of its length" and what he produces to solve it is: : mean_std ( sum2 sum inv_len -- mean std ) \ precise_mean = sum * inv_len; tuck u* \ sum2 inv_len precise_mean \ mean = precise_mean >> FRAC; dup FRAC rshift -rot3 \ mean sum2 inv_len precise_mean \ var = (((unsigned long long)sum2 * inv_len) >> FRAC) - (precise_mean * precise_mean >> (FRAC*2)); dup um* nip FRAC 2 * 32 - rshift -rot \ mean precise_mean^2 sum2 inv_len um* 32 FRAC - lshift swap FRAC rshift or \ mean precise_mean^2 sum*inv_len swap - isqrt \ mean std ; So his code is hideous and I'm wondering if we can do it better in Factor? I'd love to take a stab at it myself but I have no idea what mathematical formula he is implementing. Anyone knows? As far as I understand, given three scalar values: the sum of all elements in a vector, the sum of all elements squared and the inverse of the length, you should be able to calculate the mean of the vector and the standard deviation. -- mvh/best regards Björn Lindqvist ------------------------------------------------------------------------------ _______________________________________________ Factor-talk mailing list Factor-talk@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/factor-talk
